Hoping some of the more knowledgable folks around here could offer commentary on the remarks here? Is it as simple as the captain refused the aircraft and sent it back? Is that unusual?

Does CA mean captain? What does Mel stand for?

Thanks in advance as always.

AC0125/05JAN EQU ACA320E01
CTY TML ARR DEP GRND AIR CABINS J Y
YYZ - 1605 - 04.20
YYC 1825 TOTAL TIME YYZYYC 4.20
RMKS/DELAYED ACCOUNT MTCE MEL APPLIED ON ORIGINAL FIN 219 FOR W
HICH THE CA REFUSED TO OPERATE THE A/C.
YYZ 1756 01:51L YYC 2020 01:55L 320 MTF AD AA
DEP TML T1 GATE --/D28
ARR TML GATE --/-----